1. Field of the Invention
The present invention relates to a piezoelectric actuator, a liquid transport apparatus, and a method for producing the piezoelectric actuator.
2. Description of the Related Art
Conventionally, a piezoelectric actuator is known, which drives an object when an electric field is applied thereto to generate piezoelectric deformation of the piezoelectric actuator. For example, in the case of a piezoelectric actuator for an ink jet head described in Japanese Patent Application Laid-open No. 2009-241325 (FIG. 11), two piezoelectric layers, each of which is composed of a piezoelectric material, are stacked, wherein a common electrode is arranged between the two piezoelectric layers, and a plurality of individual electrodes (first electrodes) are arranged on a surface of one piezoelectric layer. The portion, which is interposed between the common electrode and the individual electrode of one piezoelectric layer, is polarized in the thickness direction to form an active portion, and the other piezoelectric layer functions as a vibration plate. When a voltage is applied between the individual electrode and the common electrode, then the electric field is generated in the thickness direction in the active portion of one piezoelectric layer, and the active portion is piezoelectrically deformed so that the active portion is shrunk in the in-plane direction.
In the meantime, in the case of the piezoelectric actuator for the ink jet head described in Japanese Patent Application Laid-open No. 2009-241325, the piezoelectric layer of the piezoelectric actuator is joined to a plate of a channel unit composed of a metal material by means of a thermosetting adhesive. When the temperature is returned to the ordinary temperature after heating the piezoelectric layer and the channel unit in order to cure the thermosetting adhesive, the compressive stress in the in-plane direction remains in the piezoelectric layer, due to the difference in the coefficient of linear expansion between the both. Further, the deformation amount is decreased in some cases on account of the compressive stress allowed to remain in the piezoelectric layer when it is intended to piezoelectrically deform the active portion of the piezoelectric layer. In view of the above, in the case of the piezoelectric actuator for the ink jet head described in Japanese Patent Application Laid-open No. 2009-241325, an electrode (second electrode) is arranged at a portion of the piezoelectric layer to surround the individual electrode (first electrode), and a voltage is applied to the electrode to effect the polarization in the thickness direction. Thus, the portion of the piezoelectric layer, which surrounds the active portion, is shrunk in the in-plane direction. The active portion is pulled in the in-plane direction in accordance with the shrinkage, and the remaining compressive stress is relaxed or mitigated.
However, the piezoelectric actuator described in Japanese Patent Application Laid-open No. 2009-241325 requires, for example, terminals and wiring lines which are provided to apply the voltage to the second electrodes in order to shrink the portions of the piezoelectric layer facing the second electrodes in the in-plane direction, for example, in addition to terminals and wiring lines which are provided to apply the voltage to the first electrodes in order to apply the electric field to the portions of the piezoelectric layer facing the first electrodes (drive the portions). For this reason, the number of terminals and the number of wiring lines are increased twice, and the structure or arrangement is complicated. If the terminals and the wiring lines are commonly used, the portions of the piezoelectric layer, which face the second electrodes, are also piezoelectrically deformed when the electric field is applied to the portions of the piezoelectric layer which face the first electrodes.